This is a continuation of U.S. Patent application Ser. No. 07/316,338, filed Feb. 27, 1989 02/27/89 and entitled "A Particle Separation/Classification Mechanism" now abandoned.
This invention relates generally to particle separation and, more particularly, to particle separation based upon the relative densities or weights of the particles involved.
The separation of a useful product from an unusable item has plagued man almost from the dawn of time. In fact, the early form of threshing wheat, using the wind to blow away the chaff, is one such solution to the problem.
As the industrialization of the world took place, the separation of particles became a more intense problem since the materials sought were needed in higher concentrations than before.
Separating a fluid mixture has posed some very unique problems. With these problems, some unique solutions have been developed such as U.S. Pat. No. 4,539,103, entitled "Hydraulic Separating Method and Apparatus" issued Sept. 3, 1985, to Hollingworth; and U.S. Pat. No. 4,176,749, entitled "Materials Separation" issued Dec. 4, 1979, to Wallace et al. In both of these inventions, the material that is to be separated is suspended in a liquid which is utilized for the extraction of the material.
Unfortunately, the abilities and expertise of liquid seperators are not easily ported over to a mixture of dry material.
In attempting to solve this problem, a wide variety of fluidized beds have been developed including: U.S. Pat. No. 4,194,971, entitled "Method of Sorting Fluidized Particulate Material and Apparatus Therefor" issued Mar. 25, 1980, to Beeckmans; and U.S. Pat. No. 4,546,552, entitled "Fluid Induced Transverse Flow Magnetically Stabilized Fluidized Bed" issued Oct. 15, 1985, to Cahn et al.
In all fluidized bed separation situations, the mixture to be separated is suspended on a grate or bed while air "bubbles" through the mixture at a rate sufficient to remove a targeted particle permitting the remaining material to be swept away or to fall through the grate. Balancing the inflow of contaminated mixture to the throughput is extremely difficult. Without this control though, the mechanism does not perform optimally.
The problem of control is of such a concern that a whole group of inventions address this problem alone. One such invention is described in U.S. Pat. No. 4,248,702, entitled "Stratifier Discharge Control" issued Feb. 3, 1981, to Wallace et al.
Even though the fluidized bed concept is complex, it is far from optimal and a wide range of enhancements have been developed such as U.S. Pat. No. 4,156,644, entitled "Pulsating Sludge Bed with Inclined Plates" issued May 29, 1979, to Richard.
As the complexity of the devices have grown, so too has the down time and repair costs. To attempt to simplify the situation, some devices have attempted to revert to the simpler modes of operation, or have attempted to solve the problem in unique ways. This includes U.S. Pat. No. 4,589,981, entitled "Fluidized Bed Classifier" issued May 20, 1986, to Barari et al. and U.S. Pat. No. 4,521,303, entitled "Solids Separation in Self-Circulating Magnetically Stabilized Fluidized Bed" issued June 4, 1985, to Hicks et al.
In all of these apparatuses, the mechanism becomes more and more expensive to operate and acquire. This makes them less than ideal for many situations.
Perhaps the most illustrative of the techniques currently used are the ones developed to separate tobacco leaves and parts from sand. These include: U.S. Pat. No. 4,216,080, entitled "Method and Apparatus for Separating Sand from Botanical Fines" issued Aug. 5, 1980, to Summers et al.; U.S. Pat. No. Re 29,625, entitled "Process and Apparatus for Separating Sand from Botanical Materials" issued May 9, 1978, to Summers; and, U.S. Pat. No. 3,842,978 entitled "Process and Apparatus for Separating Sand from Botanical Materials" issued Oct. 22, 1974, to Summers.
In these inventions, the contaminated mixture (tobacco fines and sand) is dropped into a fluidized bed arrangement where it is supported by a grate. Air is drawn through the grate which causes the contaminated mixture to "bubble." The heavier sand falls through the grate. The bubbling action pulls a partially cleaned mixture of sand and fines up to a cyclone separator which performs a final cleaning of the mixture.
The final cleaning by the cyclone separator is necessary since it is this cyclone separator which provides the air draft to "suck" the partially cleaned mixture from the fluidized bed.
In these inventions, the use of the fluidized bed is required since the contaminated mixture must have a certain amount of dwell time within the separating mechanism. The dwell time within the bed is necessitated by the very nature of the cyclone separator which is extremely sensitive to many factors including the feed and exhaust tubing arrangement, physical damage to the input and exhaust ports, motor speed, variations in power source, etc.
It is clear from the foregoing that except for the expensive and delicate fluidized bed arrangements, an efficient inexpensive solution to the separation of particles does not exist.